In modern mobile communications networks, most importantly in 4th Generation (4G) Long Term Evolution (LTE) networks, antenna alignment is vital for delivery of fast and reliable mobile broadband connections, correct signal propagation, and spot-on network coverage throughout the entire mobile communications base station lifecycle. In current networks, frequent antenna alignment and antenna pattern changes are required not only to increase system capacity but also to allow for a smooth network operation in time-varying traffic conditions.
Antenna adaptation for optimal cell site coverage can be accomplished by reforming the antenna radiation pattern using any of three techniques: beam tilting, beam width forming or beam steering. In beam tilting, or electro-mechanical tilt, the front and back antenna lobes tilt in same direction, and the antenna horizontal radiation pattern is shaped so as to minimize the overlapping area along with the intra- and inter-cell interference. By physically displacing the antenna panel, either via mechanically tilting or rotating the antenna, changes occur along a single horizontal plane. Therefore, as the front lobe of the antenna is tilted down, the back lobe is, by default, tilted up. By changing the width of the beam, or azimuth beam width, the antenna's radiating elements are movable. This enables components such as compensating radio frequency feed line phase shifters to provide broad range of beam width angle variation of the antenna array's azimuth radiation pattern. In beam steering (changing the beam direction, or azimuth steering or pan, the antenna is mechanically rotated about a vertical axis to provide different geographic coverage.
To provide the aforementioned functionalities for adaptation of antenna coverage, phased-array antennas arrays with embedded systems providing radiated beam adjustment are typically employed in actual applications. Such antenna arrays typically comprise a reflector and a plurality of antenna elements coupled thereto for directing a beam of electromagnetic energy in a propagation direction. The antenna may include a plurality of phase shifters operatively connected to the antenna elements, and a control device operatively connected to the phase shifters to tilt the beam propagation direction. The antenna may further include an electromechanical system coupled to the antenna reflector for rotating the latter about a vertical axis to vary signal azimuth direction. The antenna may also include an electromechanical system coupled to the antenna array for adjusting relative radiator positioning to control beam width. Furthermore, such sophisticated antenna arrays are generally retrofitted with remote antenna adjustment systems enabling accurate network alterations to be carried via the Operational Maintenance Center (OMC) irrespective of weather conditions.
Antenna mechanical tilt adjustment methods practiced in the prior art typically entail the use of a set of conventional mechanical tilt brackets. Consequently, human intervention is required, making the adjustments dangerous, labor intensive and cost-inefficient. Furthermore, these methods demonstrate skewed antenna radiation footprint coverage when the antenna is offset with respect to the antenna boresight setting due to the fact that the mechanical tilt axis lies behind the azimuth steering axis. Additionally, prior art antenna mounting brackets featuring remote down-tilt methods cannot sustain high force loads due to mechanical design limitations. Moreover, they typically employ an electromechanical actuator comprising a coupled motor and a gear set without incorporating provisions for manually adjusting the mechanical tilt of the antenna beam in case of field service or component failure. Current methods of antenna remote azimuth steering (RAS) in the prior art also do not incorporate provisions for manually adjusting the azimuth of the antenna beam in case of field service or component failure.
Also, due to the importance of accurate antenna pointing to a reference azimuth and mechanical tilt direction, in order to minimize signal quality degradation, the use of complex alignment tools and geographic landmarks or electronic alignment devices to install the antenna bracket to the boresight setting is not recommended as they fail to provide the optimal antenna alignment due to a multitude of reasons such as multipath errors, soft and hard iron disturbances, lack of alignment with the antenna back etc. . Systems providing remote azimuth steering (RAS) functionalities that retain the antenna in the desired azimuth direction solely using a high-ratio gearbox, without incorporating any provisional means of reducing stress induced to the gearbox components by rapid load changed due to external forces, may experience mechanical looseness, eccentric shafts, gear wear, broken teeth, and bearing wear.
The prior art includes several antenna support structure solutions for providing remote electrical radiated beam steering. These structures typically comprise a stationary base, an adjustable antenna mounting bracket, and a variable electrical tilt phased-array. Such an antenna support structure may comprise a rotating base coupled to the adjustable antenna mounting bracket, a motor and a gear set operatively connected to the rotating base to adjust antenna azimuth direction. The antenna support structure may further comprise an adjustable lower and an upper tilt bracket coupled to the antenna mounting bracket, a motor and a gear set operatively connected to the tilt brackets to mechanically vary antenna tilt direction.
U.S. Pat. No. 8,446,327 B2 to Vassilakis discloses a two-way terrestrial antenna that includes electrical down-tilt and azimuth adjustment capabilities. The antenna system comprises an antenna support structure, an antenna including one or more radiating elements, and an antenna mounting structure coupling the antenna to the antenna support structure. The antenna mounting structure includes a movable mount allowing change of the antenna orientation. However, effecting a deviation from the support structure along the x-axis (down-tilt) and then adjusting the antenna azimuth, i.e. rotating around the antenna z-axis, orientates the antenna in a skewed position with both tilt and roll.
This antenna system also comprises an antenna position sensor module mounted on the antenna for detecting at least one of vertical and azimuth orientation with respect to the earth's magnetic field. However, digital compasses relying on the earth's magnetic field to provide heading are subject to hard and soft iron errors, acceleration errors, and severe inclinations that increase heading calculation complexity and measurement inaccuracy. Thus, to reduce measurement inaccuracy, supplementary measurements must be made and additional precautions may be required.
In addition, the antenna heading adjustment apparatus is fully motorized and no manual operation provisions have been made. As a result, an electrical failure may risk the system's operability. Furthermore, the system is conventionally mounted to a vertically-oriented supported structure using fixed bottom and top mounting brackets. Thus, it does not provide a remotely-controlled antenna mechanical tilt adjustment mechanism.
U.S. Pat. No. 7,183,996 B2 to Wensink teaches a method of making remote plumb-to-level and compass heading adjustments of multi-antenna sectors typically found in cellular telephone networks. A helix heading adjustment apparatus, or a Pitman arm arrangement, is used to provide antenna heading adjustment according to the readings collected from an electronic compass circuit board with respect to the earth's magnetic field. However, as explained in the previous paragraph, such antenna heading adjustment techniques are not optimal. Furthermore, the system provides antenna down-tilt using a hinged lower bracket and an upper tilt bracket connected to the antenna by links. The upper tilt bracket is mounted to a vertically-translating dust cover. Vertical motion of the dust cover is translated to tilting motion of the antenna by the links. However, the system does not provide mechanical up-tilt which is often employed in mobile network design and optimization in tandem with electrical tilt to reduce signal interference between neighboring sites by greatly suppressing antenna radiation pattern side lobes. In addition, the antenna tilt and heading adjustment apparatus is fully motorized and no manual operation provisions have been made. Thus, an electrical failure may risk the system's operability. Furthermore, the antenna tilt and heading adjustment apparatus includes a mechanical breaking arrangement employing an anti-rotate lock cap and lock teeth geometry. However, this breaking arrangement may not meet the increased load requirements of advanced ultra-wideband and multi-band mobile base station antenna arrays.
U.S. Patent Application No. 2005/0,248,496 A1 to Chen et al. discloses an adjustable antenna mount that can remotely control the direction of a mobile base station antenna. The antenna mount comprises a rotating base mounted on a stationary base. Both bases comprise a suitably-aligned gear set and a motor. The motor in the rotating base rotates the vertical gear set, a horizontal shaft, a set of rotation plates, the antenna bracket and the antenna in a vertical plane. Similarly, the motor in the stationary base rotates the horizontal gear set, a vertical shaft and the rotating base in the horizontal plane. Nevertheless, the antenna mount provides provisions only for relative azimuth alignment of the antenna panel. Thus, accurate azimuth alignment with respect to True or Grid North cannot be accomplished. Furthermore, no provisions for detecting and compensating for non-vertical orientation of the antenna mount are provided. Also, despite the fact that the antenna mount includes arrangements preventing the antenna from exceeding the maximum allowable vertical travel, no such arrangements exist for the horizontal plane. It is thus apparent that in case of position sensor failure, there are no precautionary measures restricting the maximum allowable horizontal travel. In addition, the antenna mount is fully motorized and no manual operation provisions have been made. Thus, as with other systems, an electrical failure may risk the system's operability.
WO 2013/171291 A2 to Kolokotronis discloses an antenna mounting assembly and method for installing and manually or remotely adjusting the direction of cellular antennas. The antenna mounting assembly comprises a reference frame, attached to an existing base station mast using a set of conventional mechanical tilt brackets, and an antenna mounting formation comprising an antenna and upper and lower antenna mount attached thereto, enabling antenna azimuth adjustment. However, as clarified above, the antenna's tilted azimuth rotation axis, that is parallel to the reference frame tilted axis, results in an inclined orbit with respect to the horizontal plane and in an adverse skewed antenna radiation pattern. The lower antenna mount includes either a motor or a manually driven azimuth steering unit. Thus, both modes of operation cannot be combined in a single unit resulting in system operability risk in case of an electrical failure. Furthermore, the antenna assembly is mounted to the antenna support via prior art hinged top and bottom tilt brackets. Thus, it does not provide a remotely-controlled antenna mechanical tilt adjustment mechanism. Furthermore, the lower antenna mount includes an antenna locking mechanism comprising a locking plate with a series of locking holes and a manually or linearly actuated locking pin. However, this breaking arrangement requires a big radius locking plate to provide azimuth offset resolution of fine increments.
Consequently there is a need not found in the prior art for an antenna mounting bracket for use in a communications network in which both antenna direction and inclination is remotely adjustable. There is also a need for remote operation that is capable of universal antenna mounting, precise antenna boresight orientation, azimuth steering, and mechanical tilt featuring both remote and manual operating modes. There is a further need for an efficient zero backlash gear system that is able to handle increased loads.